The majority of conventionally mass-produced piezo ceramics are made from PZT (lead zirconate titanate) materials and thus contain lead. However, In recent years, the development of lead-free piezoelectric ceramics has been desired in order to eliminate the adverse influence of lead on the environment. As materials for the lead-free piezoelectric ceramics (referred to as “lead-free piezoelectric ceramic compositions”), compositions represented by the compositional formula: ANbO3 (where A is an alkali metal) such as potassium sodium niobate ((K,Na)NbO3) are proposed. However, the lead-free ANbO3 piezoelectric ceramic compositions themselves have a problem of inferior sinterability and humidity resistance.
As a measure against this problem, Patent Document 1 described below discloses a technique of adding Cu, Li, Ta, or the like to the lead-free ANbO3 piezoelectric ceramic compositions in order to improve sinterability and to eventually improve piezoelectric properties.
In addition, Patent Document 2 discloses a lead-free piezoelectric ceramic composition represented by the general formula: {Lix(K1-yNay)1-x} (Nb1-zSbz)O3 (where 0≤x≤0.2; 0≤y≤1.0; and 0≤z≤0.2 except for the case of x=z=0) and capable of achieving relatively good sinterability and piezoelectric properties.